1. Field of the Invention
The present invention relates to a demodulating device, a demodulating method and supply medium and relates in particular to a demodulating device, a demodulating method and supply medium in which data modulated simultaneous with the performing of digital sum value control for recording onto a data transmission path or recording medium is detected as recorded data, demodulated and then reproduced.
2. Description of Related Art
Data modulation for recording or transmission of data is performed when transmitting data along a specific transmission path or recording data on a recording medium such as a magnetic disk, optical disk or magneto-optical disk, etc. One method for performing this kind of modulation is known as block coding. In block coding, a data string is converted into blocks (hereafter "data words") consisting of units of m.times.i bits. This dataword is converted to codewords comprised of n.times.i bits according to an applicable code rule. This code becomes a fixed length code when i=1, and when a plurality of i are selected, or in other words when i is selected within a specified range from i through imax (maximum value of i) and converted, this code becomes a variable length code. This block encoded code is expresses as a variable length code (d, k; m, n; r).
Here, i is called a restriction length and imax becomes r (maximum restriction length) The minimum run d shows the minimum number of consecutive "0"s within consecutive "1"s in a code string. The maximum run k shows the maximum number of consecutive "0"s within consecutive "1"s in a code string.
However in the above mentioned variable length code, NRZI (Non Return To Zero Inverted) modulation is performed in which the "1" for a variable length code is inverted while a "0" is not inverted when for instance recording on optical disks and magneto-optical disks such as compact discs and minidiscs. In this process, recording is performed based on this NRZI modulated variable length code (hereafter recorded wavelengthstring). Another system records the modulated bit string as is without using NRZI modulation for instance on magneto-optical disks to ISO standards.
Various modulation methods have been proposed. For instance, in order to perform high density recording in a direction of linear velocity when Tmin is set at the minimum inversion interval and Tmax is set as the maximum inversion interval of a recorded waveform string, the minimum inversion interval Tmin is preferably long, in other words the minimum run d should be large. In order to reproduce the clock pulse, the maximum inversion time T is preferably short, in other words, the maximum run k is preferably small.
More specifically, modulation methods are known for use with optical disks, magnetic disks, or magneto-optical disks. Such methods are referred to as variable length RLL(1-7), fixed lengy RLL (1-7) and variable length RLL (2-7), etc.
The conversion table for the fixed length RLL (1-7) code is as follows.
TABLE 1 RLL (1, 7; 2, 3; 2) Data Code i = 1 11 00x 10 010 01 10x i = 2 0011 000 00x 0010 000 010 0001 100 00x 0000 100 010
The symbol x shown in the conversion table is set as 1 when the subsequent channel bit is 0. The symbol x is set as 0 when the subsequent channel bit is 1. The restriction length r is 2.
The parameters for the variable length RLL (1-7) are (1, 7; 2, 3; 2). The minimum inversion interval Tmin is 2(=1+1)T when the bit interval for the recorded waveform string is set as T. Also, when the bit interval of the data string is set as Tdata, the minimum inversion interval Tmin becomes 1.33 (=(2/3).times.2) Tdata, the maximum inversion interval Tmax becomes 8T (5.33Tdata). Further, the detection window width Tw is shown (m/n) x Tdata and the value of Tw as 0.67 (=2/3).
In the channel bit string on which modulation was performed with RLL (1-7), the occurrence frequency for Tmin is greatest as 2T and then 2T and 3T in order of frequency of occurrence. Clock reproduction is generally more effective if many periods occur in which edge information occurs early such as with 2T and 3T. However waveform distortion is more prone to occur if 2T repeatedly occurs. In other words, the output waveform for 2T is small and easily susceptible to the effects of defocusing and tangential tilt. Further, recordings with a minimum mark that repeats are easily susceptible to external disturbances such as noise when recording at a high linear density and mistakes are prone to occur in reproducing data.
Whereupon, the inventors proposed a method in Patent Application No. Hei 9-256745 for coding to restrict continuous Tmin. This method is referred to as RML coding (or Repeated Minimum Run-Length Limited Code).
In this proposed method, when the variable length code (d, k, m, n; r) is for instance a variable length code (1, 7; 2, 3; 3), or in other words when d which is the minimum run of 0 is 1 bit, k which is the maximum run of 0 is 7 bits, m which is the maximum data length is 2 bits, n which is the basic code length is 3 bits, and r which is the maximum restriction length is 3, then the resulting conversion table is as shown below.
TABLE 2 RML (1, 7; 2, 3; 3) Data Code i = 1 11 00x 10 010 01 10x i = 2 0011 000 00x 0010 000 010 0001 100 00x 0000 100 010 i = 3 100110 100 000 010
restriction length here is 3.
When the data string has become "10", in Table 2 and in particular when the next four bits of data are referred to so that the htotal 6 bit data string is "100110", a special code can be provided to match this data string and limit the repetition of the minimum run to a maximum of five times by the modulation in Table 2.
The above method allows stable recording and reproduction of data at high linear density.
However coding modulation that matches the medium (transmission) is performed during recording onto a recording medium or transmission of data, but when a direct current component is contained in this modulation coding, fluctuations are prone to occur in all types of error signals such as in tracking errors for servo control of disk devices. Accordingly this direct current component should be omitted as much as possible.
DSV (digital sum value) control was not performed in the modulation coding shown here for the variable length RLL (1-7) table and the RML (1-7) table. In these kind of cases, a specified DSV control bit is inserted into a coding string (channel bit string) for a specified interval of a coded string after modulation and DSV control can then be performed.
The term DSV (digital sum value) indicates the performing of NRZI on the channel bit string (in other words level coding) and the sum then obtained from adding a +1 to the "1" of that bit string and a -1 to the "0". The DSV is a guide for the direct current component of the coding string. The direct current component of the code string is restricted by making the absolute value of the DSV smaller.
The DSV control bit to be input here is: EQU 2.times.(d+1)
In other words, when d=1, then 2.times.(1+1) can be made equal to 4 bits. The minimum run and maximum run can be maintained in the desired interval and inverted or non-inverted DSV control can be fully performed.
The DSV control bit is essentially a redundant bit so that from the point of view of code conversion efficiency, the DSV control bit should be as small as possible.
Here, if for instance the control bit is 1.times.(d+1) or in other words, when d=1, then 1.times.(1+1) can be made equal to 2 bits. In this case, inverted or non-inverted DSV control can be fully performed in the desired interval. The minimum run will be maintained unchanged however the maximum run will become long and become (k+2). The minimum run must be maintained unchanged for coding purposes but the maximum run need not always be protected. In some cases a pattern disrupting the maximum run is present in a format used in the synchronizing signal. In EFM plus used in DVD for instance, the maximum run is 11T but 14T is actually allowed due to the circumstances of the format.
Thus, as related above, when recording data on a recording medium such as magnetic disks, magneto-optical disks or optical disks recorded at high density and utilizing RLL (1-7) and RML (1-7) which are conversion tables not incorporating DSV control, and DSV bits were then inserted as a channel bit string with DSV control. Up until now there was the problem that when d=1, insertion of DSV bits of less than 4 bits caused the maximum run to increase.
Further, in the same way, the inserted DSV bit was a redundant bit for a recording code making it necessary for control to be performed with as few bits as possible.